<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=\, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <link rel="stylesheet" href="bootstrap/css/bootstrap.css">
    <style>
        .nav{
            width: 70%;
            height: 400px;
            margin-left: auto;
            margin-right: auto;
        }
        .nav>div{
            padding: 20px;
        }
        .nav>div>img{
            width: 100%;
            height: 100%;
        }
    </style>
</head>
<body>
    <div class="nav">
        <div class="col-md-4 col-sm-6 col-xs-12"><img src="images/item01.jpg" alt=""></div>
        <div class="col-md-4 col-sm-6 col-xs-12"><img src="images/item02.jpg" alt=""></div>
        <div class="col-md-4 col-sm-6 col-xs-12"><img src="images/item03.jpg" alt=""></div>
        <div class="col-md-4 col-sm-6 col-xs-12"><img src="images/item04.jpg" alt=""></div>
        <div class="col-md-4 col-sm-6 col-xs-12"><img src="images/item05.jpg" alt=""></div>
        <div class="col-md-4 col-sm-6 col-xs-12"><img src="images/item06.jpg" alt=""></div>
    </div>
</body>
</html>